A number of evaluation and monitoring systems have been disclosed within various industries for measuring the properties during and after formation of certain materials, using radiofrequency signals. The surface characteristics, internal homogeneity, thickness, and rate of erosion of a material are some of the important attributes that may require monitoring and evaluation.
On a bigger scale, some industries such as the glass, steel, and plastic industries use large furnaces to melt the raw material used for processing. These furnaces may reach a length equivalent to the height of a 20-story building. Thus, they are a key asset for manufacturers in terms of costs and operational functionality. In order to minimize the internal heat loss at high operating temperatures, these furnaces are constructed using refractory material, having very high melting temperatures and good insulation properties, to create a refractory melting chamber. However, the inner walls of the refractory chamber of the furnace will degrade during operation. The effects of this degradation include inner surface erosion, stress cracks, and refractory material diffusion into the molten material.
In particular, the use of microwave signals to measure the thickness of materials such as furnace walls have been addressed in the prior art, as described in U.S. Pat. No. 6,198,293 to Woskov et al. and U.S. Pat. No. 9,255,794 to Walton et al., the specifications of which are incorporated herein by reference in their entireties. However, these efforts have faced certain challenges and limitations. In particular, attempts made to determine furnace wall thickness on hot furnaces have been generally unsuccessful because of the large signal losses involved in evaluating the inner surface of refractory materials, especially at relatively high frequency bands. Likewise, at relatively low frequency bands signals still experience losses and are limited in terms of the bandwidth and resolution required by existing systems.
Moreover, in placing system components close to the surface of the refractory material to be evaluated, spurious signal reflections make it difficult to isolate the reflected signal of interest, thus further complicating the evaluation of the status of either the inner surface or the interior of such materials. A major challenge is that furnace walls become more electrically conductive as temperature increases. Therefore, signals going through a hot furnace wall experience significant losses making the detection of these signals very challenging.
Additional efforts have been made to evaluate the status of a material, using electromagnetic waves, by reducing the losses and level of spurious signals involved in evaluating refractory materials, as described in U.S. Pat. App. No. 20150362439 by Bayram et al. and U.S. Pat. App. No. 20150276577 by Ruege et al., the specifications of which are incorporated herein by reference in their entireties. However, these systems are primarily aimed to mitigate multiple reflection effects of the electromagnetic waves used for suppression of clutter associated with the received signal. In addition, these attempts have focused on standalone systems lacking integration as a single solution, further requiring software for maximizing the extraction of information from the measured data, and facing challenges to access areas of difficult access in an industrial environment. As a result, these systems are not able to monitor and evaluate a large asset, such as an industrial furnace, for optimizing its operational life, without the support of tracking and software tools.
Currently, there is no well-established integrated system of deterministically and effectively measuring the rate of penetration of molten material into the surrounding refractory material to optimize both the operational life and the maintenance plan of the furnace. As a result, manufacturers experience either an unexpected leakage of molten material through the furnace wall or conservatively shut down the furnace for re-build to reduce the likelihood of any potential leakage, based on the manufacturer's experience of the expected lifetime of the furnace. The lifetime of a furnace is affected by a number of factors, including the operational age, the average temperature of operation, the heating and cooling temperature rates, the range of temperatures of operation, the number of cycles of operation, and the type and quality of the refractory material as well as the load and type of the molten material used in the furnace. Each of these factors is subject to uncertainties that make it difficult to create accurate estimates of the expected lifetime of a furnace.
Moreover, the flow of molten material, such as molten glass, at high temperatures erodes and degrades the inner surface of the refractory material and creates a high risk for molten glass leakage through the refractory wall. A major leak of molten glass through the gaps and cracks in the furnace walls may require at least 30 days of production disruption before the furnace can be restored to operating mode because it needs to be cooled down, repaired, and fired up again. Furthermore, a leak of molten glass may cause significant damage to the equipment around the furnace and, most importantly, put at risk the health and life of workers. For these reasons, in most cases furnace overhauls are conducted at a substantially earlier time than needed. This leads to significant costs for manufacturers in terms of their initial investment and the reduced production capacity over the operational life of the furnace.
Another important issue is that the material used to build the refractory chamber of the furnace may have internal flaws not visible by surface inspection. This could translate into a shorter life of the furnace and pose serious risks during furnace operation. Accordingly, on the one hand the refractory material manufacturer would like to have a means to evaluate the material during manufacture to be able to qualify the material for furnace construction following quality standards to deliver material with no flaws. On the other hand, the customer purchasing the refractory material would like to have a means for performing internal inspections of such material before constructing a furnace.
Thus, there remains a need in the art for systems capable of remotely evaluating the status of such refractory materials, through measurements of propagating radiofrequency signals that avoid the problems of prior art systems.